The present invention relates to a body frame structure of a vehicle, particularly of a straddle-type vehicle for traveling on rough ground and also relates to a method of manufacturing the same.
A straddle-type vehicle is generally a small-sized vehicle suitable for traveling on a rough ground, and such vehicle is, for example, provided with a front wheel and a lateral pair of rear wheels. A rider straddles a rider""s seat positioned at an upper portion of a vehicle body frame and steers a front wheel by operating a steering handle, and the vehicle runs through the driving of an engine mounted to the vehicle body frame.
Such body frame or frame structure of a vehicle is usually composed by interconnecting, by using coupling members, a plurality of lateral paired pipe or tube members each extending from the front portion towards the central portion of the vehicle so as to provide an integral frame structure, and then, a support bracket of a suspension device of a wheel or a reinforcing bracket is welded.
However, in the case of the frame structure of the vehicle body mentioned above, it is difficult to access or insert a welding torch or like into a frame structure at the time of welding a bracket or like member to the frame structure at the inside thereof and also difficult to automatically carry out the welding process by, for example, utilizing a robot. Thus, it is difficult to provide a good welding performance, which may increase working cost.
Moreover, since the brackets or like are welded after the construction of the frame structure, it is also difficult to reform deformation caused after the welding.
Furthermore, it is necessary to newly prepare a welding jig or like every time the change or modification of a specification or a model of an engine to be mounted or suspension stroke, which requires an increased cost.
An object of the present invention is to substantially eliminate defects or disadvantages encountered in the prior art mentioned above and to provide a vehicle body frame having an improved structure suitable for easy assembling and manufacturing thereof and for achieving improved workability.
This and other objects can be achieved according to the present invention, in one aspect, by providing a frame structure of a body of a vehicle in which a front wheel, which is steered, is disposed in front of a vehicle body frame and a rear wheel disposed to the rear side thereof, an engine is arranged between the front and rear wheels, and a rider""s seat is disposed at a rear upper portion of the vehicle body frame, said vehicle body frame structure comprising:
a front frame unit provided with a support member for a front wheel suspension device and a support member for a steering shaft;
a center frame unit provided with a support member for a rear wheel suspension device and an engine mounting member; and
a rear frame unit supporting the rider""s seat,
the front, center and rear frame units being assembled respectively individually and then coupled together integrally.
Further, it is to be noted that term xe2x80x9cfrontxe2x80x9d, xe2x80x9crearxe2x80x9d, xe2x80x9cupperxe2x80x9d, xe2x80x9clowerxe2x80x9d and the like used herein are referred with reference to a vehicle in a normal standing (running) state or a state illustrated in the accompanying drawings which will be mentioned hereinlater.
In a preferred embodiment, the front frame unit comprises a lateral pair of flat front main frame members and a coupling member disposed so as to bridge the front main frame members, the support member of the front wheel suspension device is mounted to the front main frame members, and the support member of the steering shaft is mounted to the coupling member of the front frame unit.
The center frame unit also comprises a lateral pair of flat center main frame members, each having a horizontally curved U-shape so as to surround the engine from a vertical side and a rear side, and a coupling member disposed between the center main frame members so as to integrally couple the center main frame members, the support member of the rear wheel suspension device is provided for the center main frame members and the engine mounting member is provided for the coupling member disposed between the center main frame members.
The center main frame members include center lower tubes, respectively, which have rear half portions extending obliquely rearward upward, rear ends of the extended rear half portions of the center lower tubes are connected to substantially central lower portions of seat rail tubes constituting the rear frame unit to thereby constitute the rear half portions of the center lower tubes as support members of the seat rail tubes, and a rear cushion bracket supporting a rear cushion unit of the rear wheel suspension device is provided for a coupling member disposed so as to bridge rear end portions of the center lower tubes. The front frame unit includes coupling members disposed to vertical rear end portions of the front main frame members so as to connect the front main frame members and the vertical front end portions of the center main frame members of the center frame unit are coupled to the front frame unit through the coupling members of the front frame unit.
The front main frame members of the front frame unit are connected, at an upper end thereof, to each other through the upper coupling member, to which the support member of the steering shaft is attached. Furthermore, the front main frame members of the front frame unit are connected, at a lower end thereof, to each other through the lower coupling member, to which the engine mounting member is attached.
A lateral distance of the lower portion of the center frame unit is formed to be wider than a lateral distance of the lower portion of the front frame unit, the lower rear end portions of the front main frame members are connected to inside portions at both ends of the lower coupling member, the lower front end portions of the center frame unit are disposed so as to extend forward from the lower coupling member, the lower front portion of the center frame unit is bent inside in a width direction thereof, and the front end portion of the bent portion is connected to the rear end of the lower portion of the center frame unit from the outside in the width direction so that the connecting portions between the lower portion of the front frame unit, the lower portion of the center frame unit and the lower coupling member provide substantially a triangular shape in a plan view.
In another aspect, there is also provided a method of manufacturing a body frame structure of a vehicle in which a front wheel, which is steered, is arranged in front of a vehicle body frame, a rear wheel is arranged on a rear side of the vehicle body frame, an engine is arranged between the front and rear wheels, and a rider""s seat is disposed at a rear upper portion of the vehicle body frame, the manufacturing method comprising the steps of:
preparing a front frame unit provided with a support member of a front wheel suspension device and a support member of a steering shaft, center frame unit provided with an engine mounting member and a rear frame unit supporting the rider""s seat, the front, center and rear frame units being assembled independently; and
coupling integrally these front, center and rear frame units after being assembled independently.
In this method, the front frame unit is composed of a pair of lateral flat front main frame members which are coupled through a coupling member disposed therebetween after mounted with a bracket, a stay, a reinforcing member and the like member. The center frame unit is also composed of a pair of lateral flat front main frame members which are coupled through a coupling member disposed therebetween after mounted with a bracket, a stay, a reinforcing member and the like member.
According to the embodiments of the present invention mentioned above,
The vehicle body frame (structure) is constructed by coupling the front frame unit, the center frame unit and the rear frame unit, which are preliminarily independently assembled per each unit and then assembled and coupled together. According to such assembling or manufacturing method, since each of the frame units is relatively small size, a welding torch or like jig is easily assessed and inserted inside the unit at the time of welding the respective frame units, and making possible to operate automatically such as by utilizing a welding robot, thus improving welding, assembling and like workability and reducing manufacturing cost.
Moreover, since the respective frame units are independently assembled and then coupled together, it is not necessary to move or transfer the frame, as the entire frame structure, having relatively large size at an intermediate working time, thus reducing working labor.
Furthermore, since the frame structure is coupled (for example, welded) after the respective frame units have been assembled, less welding strain is caused after the welding and, if caused, such welding strain will be easily removed.
Still furthermore, even in a case where the design change or modification of specification of, for example, an engine or a suspension stroke of a vehicle be required, it is not necessary to disassemble or change all the frame units and necessary only to change a required one frame unit, improving the working performance.
Moreover, the front and center frame units are composed by a lateral pair of flat front main frame members, center main frame members and a plurality of coupling members disposed between these members. The respective main frame members are coupled together after the assembling of brackets, stays, reinforcing members and the like members, so that the working efficiency in the welding, assembling and like workings can be improved and automatic welding will be advantageously applicable.
Furthermore, since the support members of the steering shaft are provided for the coupling members connecting the lateral front main frame members, the axis of the steering shaft can be easily adjusted and the remedy of the welding strain can be also easily made.
Still furthermore, since the center lower tube, the front lower tube and the front engine mounting tube are connected so as to provide substantially a triangular shape in a plane view, the rigidity of the vehicle body frame structure can be made strong.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions with reference to the accompanying drawings.